Water used by humans is classified into two major types: soft water and hard water. So-called surface water, such as rainwater, and distilled water are classified as soft water to be relatively pure and have a relatively low hardness due to its composition with major components of hydrogen and oxygen. By contrast, ground water is classified as hard water to have high hardness due to its components of calcium ions (Ca2+) and magnesium ions (Mg2+).
Currently, tap water supplied to a home is hard water as it has a high content of positively charged ions, such as calcium and magnesium. Tap water also contains chlorine (Cl), which is used in a water cleaning process, as well as heavy metals, such as iron (Fe), copper (Cu), tin (Sn), zinc (Zn) and mercury (Hg), from polluted environments and water being transported via old pipes. These heavy metals bind to the fatty acids of soaps. For humans, the resulting products are not lethal but harmful. Further, they can stimulate skin aging and cause skin troubles, such as atopic dermatitis.
To resolve these problems, water softeners are widely used, which soften hard water, such as tap water to give high quality water by substituting calcium ions and magnesium ions contained in hard water with harmless sodium ions (Na+). For this softening function, a water softener typically comprises essentially a water softening tank to soften raw water, which is filled with an ion exchange resin of a particular polymer compound with sodium ions, and a regeneration tank to regenerate the ion exchange resin in which sodium ions are reduced by continuous contact with raw hard water, which contains a regeneration material for the ion exchange resin, such as salts which release sodium ions when dissolved in water.
In detail, referring to FIG. 1 which schematically shows a conventional water softener, the conventional water softener comprises a water softening tank 2 containing an ion exchange resin and a regeneration tank 12 containing a regeneration material for the ion exchange resin. The water softening tank 2 and the regeneration tank 12 are, in upper parts thereof, equipped respectively with first and second water inflow tubes 4 and 14 to transport external raw water thereto. A water discharge tube 6 is provided to a lower part of the water softening tank 2. The water softening tank 2 is, in an upper part thereof, connected to a lower part of the regeneration tank 12 via a connection tube 16. Also, first and second control valves V1 and V2 are provided respectively on the first and second water inflow tubes 4 and 14, and third and fourth control valves V3 and V4 are provided respectively on the water discharge tube 6 and the connection tube 16. When the first control valve V1 is opened, raw water is supplied to the water softening tank 2 through the first water inflow tube 4 and is softened therein. Subsequently, when the third control valve V3 is opened, the softened water is discharged to the exterior via the water discharge tube 6.
On the other hand, when water softening is carried out for a long period, concentration of sodium ions in the ion exchange resin are diminished. Thus, the resin should be periodicly regenerated. For this resin regeneration, the first and third control valves V1 and V3 are closed, and the second control valve V2 is opened to supply raw water to the regeneration tank 12. Then, the fourth control valve V4 is opened to supply the resulting water containing salt from the regeneration tank 12 to the water softening tank 2. Thereafter, the fourth control valve V4 is closed, and the third control valve V3 is opened, to completely remove salt remaining in a free form in the water softening tank 2. The resin is again available for the production of soft water.
According to the intended use, the water softening tank 2 may be provided in the number of two. Two water softening tanks may be supplied with warm and cool raw water, respectively. To separately regenerate ion exchange resins in the two water softening tanks 2, the regeneration tank 12 may be also provided in the number of two. Korean Pat. Application Nos. 1997-003670 and 2000-0039303 disclose water softeners which are similar in the technical base to, but just slightly differ in the number of and the connection method of the water softening tank and the regeneration tank from, that described above.
However, the conventional water softeners have disadvantages, as follows. The regeneration process of ion exchange resins is time-consuming because of its complexity as it requires a lot of time, even by skilled persons. Also, the conventional water softeners are very inconvenient in use because a plurality of valves (like the V1, V2, V3 and V4 as described above) should be manually controlled by a user during the resin regeneration process. For this complex structure, the conventional water softeners easily become inoperable or are often abnormally operated, require high production costs, and are large in size, and thus, require wide areas upon installation, resulting in difficult installations at narrow places, such as bathrooms.
The disadvantages of the conventional water softeners further include that, since the temperature of the generated soft water depends on the externally supplied raw water, soft water at a desired temperature is slowly supplied to a user.